Control apparatus to divide other communication apparatuses into multiple groups for slots allocated

ABSTRACT

A communication control apparatus that performs wireless communication with a plurality of communication apparatuses, the communication control apparatus comprises: a grouping unit adapted to group the plurality of communication apparatuses based on the relative positions of each of the plurality of communication apparatuses; a notification unit adapted to notify each of the plurality of communication apparatuses of the group to which that communication apparatus belongs and of a communication slot allocated to that group; and a transmission unit adapted to transmit transmission data at a predetermined timing.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a communication control apparatus and acontrol method thereof, a communication apparatus and a control methodthereof, a wireless communication system, a program, and a storagemedium.

2. Description of the Related Art

Technology that aims to configure plural connection links through relaytransmission and carry out wireless transmission with a remotecommunication terminal is known (Japanese Patent Laid-Open No. H8-97821;Japanese Patent Laid-Open No. 2001-189971). Specifically, a wirelesscommunication system is known in which address information, relayinformation, and the like are added to communication data andtransmitted to multiple addresses, and relay terminals relay the data inaccordance with the address information, relay information, and thelike.

Furthermore, a wireless communication scheme that aims to expand thecommunication range of a receiving terminal through plural senderstransmitting identical data is known (Japanese Patent Laid-Open No.H11-122150). Specifically, a scheme is known in which pluraltransmission signals, to which have been added respectively differingamounts of delay, are transmitted from plural transmission terminals; onthe receiving side, the received signal unaffected by interference isselected, equalization processing is performed thereon, and the originaldata is thereby estimated.

Furthermore, as technology for efficiently transmitting data wirelesslyto a remote communication terminal, a scheme is known in which a relayterminal having a good condition of communication is selected and datais distributed to peripheral communication terminals by way of thatrelay terminal, thereby realizing efficient data transfer (JapanesePatent Laid-Open No. 2003-332977).

However, in recent years, where data communication functionality hasbecome widespread, demand has increased for what is known as “real-time”communications, in which video data, audio data, and the like istransmitted from a data storage device through a communication line andis received and reproduced by a video display device, an audioreproduction device, or the like.

Schemes such as the above-mentioned conventional schemes respond to theoccurrence of disconnections and interruptions in the communication pathcaused by some kind of problem in the communication path by performingretransmission, changing paths, and so on. However, the retransmissionprocessing, processing for changing paths, and so on are performedasynchronously, and thus transmission delay cannot be guaranteed. Forthis reason, when stream data that is temporally continuous, such asvideo or audio, is transmitted and continuously reproduced on thereceiving side, and disconnections or interruptions occur in thecommunication path, there are situations where data underruns occur onthe receiving side. Therefore, there is a problem that the reproducedvideo is unstable, the reproduced audio cuts out intermittently, and soon.

In the abovementioned conventional schemes, by using plural paths,reception can be carried out properly even if disconnections orinterruptions occur in a single path. However, these processes assumepredetermined plural transmission terminals and a single receivingterminal, and does nothing more than implement the connection of pluralpaths by eliminating signal interference from the plural transmissionterminals. For this reason, when performing data transfers in unison toplural receiving terminals, such as with multi-channel stream data,mutual interference arises when data is transmitted to the respectivereceiving terminals over plural paths.

SUMMARY OF THE INVENTION

Having been conceived in light of the aforementioned problems, it is anobject of the present invention to provide a technique for reducing theoccurrence of disconnections and interruptions when transmitting datasuch as stream data that is temporally continuous, such as video oraudio. It is furthermore an object of the present invention to provide atechnique for avoiding mutual interference even when simultaneouslysending plural pieces of data to plural receiving terminals.

According to one aspect of the present invention, a communicationcontrol apparatus that performs wireless communication with a pluralityof communication apparatuses, the communication control apparatuscomprises:

a grouping unit adapted to group the plurality of communicationapparatuses based on the relative positions of each of the plurality ofcommunication apparatuses;

a notification unit adapted to notify each of the plurality ofcommunication apparatuses of the group to which that communicationapparatus belongs and of a communication slot allocated to that group;and

a transmission unit adapted to transmit transmission data at apredetermined timing.

According to another aspect of the present invention, a communicationapparatus that performs wireless communication in a wirelesscommunication system that includes a plurality of communicationapparatuses and a communication control apparatus, the communicationapparatus comprises:

a notification receiving unit adapted to receive, from the communicationcontrol apparatus, a notification of the group to which thecommunication apparatus belongs and a communication slot allocated tothat group;

a data receiving unit adapted to receive transmission data from anexternal apparatus and store the received data in a storage device;

a maximum likelihood processing unit adapted to perform maximumlikelihood processing on the transmission data stored in the storagedevice; and

a transmission unit adapted to transmit the transmission data on whichthe maximum likelihood processing has been performed using thecommunication slot allocated to the group to which the communicationapparatus belongs.

According to still another aspect of the present invention, a wirelesscommunication system comprising a plurality of communication apparatusesand a communication control apparatus,

wherein the communication control apparatus includes:

a grouping unit adapted to group the plurality of communicationapparatuses based on the relative positions of each of the plurality ofcommunication apparatuses;

a notification unit adapted to notify each of the plurality ofcommunication apparatuses of the group to which that communicationapparatus belongs and of a communication slot allocated to that group;and

a transmission unit adapted to transmit transmission data at apredetermined timing, and

each of the communication apparatuses includes:

a notification receiving unit adapted to receive, from the communicationcontrol apparatus, a notification of the group to which thecommunication apparatus belongs and a communication slot allocated tothat group;

a data receiving unit adapted to receive the transmission data from anexternal apparatus and store the received data in a storage device;

a maximum likelihood processing unit adapted to perform maximumlikelihood processing on the transmission data stored in the storagedevice; and

a transmission unit adapted to transmit the transmission data on whichthe maximum likelihood processing has been performed using thecommunication slot allocated to the group to which the communicationapparatus belongs.

According to yet another aspect of the present invention, a controlmethod for a communication control apparatus that performs wirelesscommunication with a plurality of communication apparatuses, the methodcomprises:

grouping the plurality of communication apparatuses based on therelative positions of each of the plurality of communicationapparatuses;

notifying each of the plurality of communication apparatuses of thegroup to which that communication apparatus belongs and of acommunication slot allocated to that group; and

transmitting transmission data at a predetermined timing.

According to still yet another aspect of the present invention, acontrol method for a communication apparatus that performs wirelesscommunication in a wireless communication system that includes aplurality of communication apparatuses and a communication controlapparatus, the method comprises:

receiving, from the communication control apparatus, a notification ofthe group to which the communication apparatus belongs and acommunication slot allocated to that group;

receiving transmission data from an external apparatus and storing thereceived data in a storage device;

performing maximum likelihood processing on the transmission data storedin the storage device; and

transmitting the transmission data on which the maximum likelihoodprocessing has been performed using the communication slot allocated tothe group to which the communication apparatus belongs.

Further features of the present invention will become apparent from thefollowing description of exemplary embodiments (with reference to theattached drawings).

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram illustrating an example of a configuration of anetwork that includes a wireless communication apparatus.

FIG. 2 is a block diagram illustrating an internal configuration of acontrol terminal.

FIG. 3 is a block diagram illustrating an internal configuration of anode.

FIG. 4 is a diagram schematically illustrating the difference in thesignal transmission range between the DSSS and OFDM techniques.

FIG. 5 is a diagram illustrating a detailed configuration of a wirelesstransmission unit and a wireless receiving unit of a control terminal.

FIG. 6 is a diagram illustrating a detailed configuration of a wirelesstransmission unit and a wireless receiving unit of a node.

FIG. 7 is a flowchart illustrating an operational procedure performed bya control terminal.

FIGS. 8A and 8B are time slot diagrams illustrating operations of acontrol terminal.

FIG. 9 is a flowchart illustrating a processing procedure performed byeach node.

FIGS. 10A, 10B, 10C, and 10D are diagrams conceptually illustrating thechange over time of the transmission of stream data by the controlterminal and nodes.

FIG. 11 is a diagram illustrating transmission of stream data by thecontrol terminal and nodes on the time axis.

FIG. 12 is a diagram illustrating procedures for node topologydetermination processing performed by a control terminal and by nodes.

FIG. 13 is a diagram schematically illustrating a relationship betweenthe strength of a received training signal and the distance betweennodes.

FIG. 14 is a diagram schematically illustrating the estimation of apositional relationship through the triangulation method.

FIG. 15 is a diagram schematically illustrating a configuration of anetwork when there is a single group.

FIG. 16 is a diagram schematically illustrating a configuration of anetwork when there are two groups.

FIG. 17 is a flowchart illustrating a procedure for processing performedby the control terminal to determine groups and time slots.

FIG. 18 is a diagram illustrating transmission of stream data by thecontrol terminal and nodes on the time axis in the case where controlinformation has been added to a beacon signal.

DESCRIPTION OF THE EMBODIMENTS

Hereinafter, embodiments of the present invention shall be described indetail with reference to the appended drawings. Note that theconstituent elements denoted in the following embodiments are onlyexamples, and the scope of the present invention is not intended to belimited thereto.

Embodiment 1 Network Configuration

FIG. 1 is a diagram illustrating an example of a configuration of anetwork that includes a wireless communication apparatus according tothe present embodiment. In FIG. 1, 101-109 are nodes (communicationapparatuses) a through i, which are the wireless communicationapparatuses according to the present embodiment; 110 is a controlterminal (communication control apparatus), which is a wirelesscommunication apparatus; and 111 is a data source that outputs AV(audio-visual) data. 112 is a group 1, made up of nodes a to c; 113 is agroup 2, made up of nodes d to f; and 114 is a group 3, made up of nodesg to i.

The data source 111 is an apparatus that outputs AV data to be processedin real time. The data source 111 continuously outputs AV data, such asmulti-screen video data, multi-channel audio data, and so on.

The control terminal 110 mutually exchanges control signals, controldata, and the like wirelessly with the nodes a 101 to i 109.Furthermore, the control terminal 110 converts AV data from the datasource 111 into stream data and wirelessly transmits the result.

The nodes a 101 to i 109 mutually communicate control signals, controldata, and the like with the control terminal 110 wirelessly.Furthermore, the nodes a 101 to i 109 wirelessly receive stream datafrom the control terminal 110 and from plural other nodes, andwirelessly transmit the received stream data.

Group 1 (112) to group 3 (114) are groups configured of plural nodes.Group allocation is determined by the control terminal 110, and eachnode is notified thereof by the control data. As shall be explainedlater, nodes within the same group each transmit stream data wirelesslyat the same timing.

(Control Terminal)

FIG. 2 is a block diagram illustrating an internal configuration of thecontrol terminal 110. In FIG. 2, 201 is a wireless transmission unit,202 is a wireless receiving unit, 203 is a control unit that controlsthe overall operations of the control terminal 110, 204 is an encodingunit, 205 is a memory, 206 is a cycle timer, and 207 is an antenna.

The control unit 203 sends control data to the wireless transmissionunit 201 via the memory 205, and controls the wireless transmission unit201 to modulate the control data into a wireless signal and wirelesslytransmit the resultant from the antenna 207. Additionally, AV data fromthe data source 111 is converted into stream data by the encoding unit204 and is temporarily stored in the memory 205. Then, in accordancewith instructions from the control unit 203, and in synchronization withthe cycle timer 206, the control terminal 110 converts the stream datainto frames, the units of transmission data, and the resultants are sentfrom the memory 205 to the wireless transmission unit 201. After this,in accordance with instructions from the control unit 203, and insynchronization with the cycle timer 206, the wireless transmission unit201 modulates the data from the memory 205 into a wireless signal, andwirelessly transmits the resultant from the antenna 207.

In accordance with instructions from the control unit 203, the wirelessreceiving unit 202 receives the wireless signal from the antenna 207,demodulates the wireless signal into received data, and sends thereceived data to the control unit 203. In addition to performing overallcontrol, the control unit 203 writes a synchronization signal, forcontrolling the synchronization of wireless communication with othernodes, into the memory 205, and performs control so that thesynchronization signal is transmitted from the wireless transmissionunit 201 at a prescribed timing. Furthermore, the control unit 203converts the transmission data into frames in accordance with terminalinformation communicated from other nodes as control data.

Detailed descriptions of the wireless transmission unit 201 and thewireless receiving unit 202 shall be provided later. In the presentembodiment, the wireless transmission unit 201 of the control terminal110 includes a DSSS type modulation unit and an OFDM type modulationunit. These two techniques utilize techniques compliant with IEEE 802.11and IEEE 802.11a, as standardized by the IEEE, and thus detaileddescriptions thereof shall be omitted. Note that “DSSS” is anabbreviation of “Direct Sequence Spread Spectrum”, whereas “OFDM” is anabbreviation of “Orthogonal Frequency Division Multiplexing”. “IEEE” isan abbreviation of “Institute of Electrical and Electronics Engineers”.

In addition, the wireless receiving unit 202 of the control terminal 110includes a DSSS type demodulation unit. The OFDM type modulation unit isused when stream data stored in the memory 205 is transmitted from theencoding unit 204. When transmitting and receiving other data, the DSSStype modulation unit and demodulation unit are used.

(Nodes)

FIG. 3 is a block diagram illustrating an internal configuration of thenode a 101. Nodes b 102 to i 109 have the same configuration. In otherwords, although the node a 101 shall be described hereinafter, thesedescriptions also apply to the nodes b 102 to i 109. In FIG. 3, 301 is awireless transmission unit, 302 is a wireless receiving unit, 303 is acontrol unit that controls the operations of the node, 304 is a memory,305 is a maximum likelihood processing unit, 306 is a decoding unit, 307is a cycle timer, and 308 is an antenna.

The wireless receiving unit 302 transmits, to the wireless transmissionunit 301, a synchronization signal notifying the symbol synchronizationtiming of the received data. Additionally, in accordance withinstructions from the control unit 303, and in synchronization with thecycle timer 307, the wireless receiving unit 302 stores the receiveddata in the memory 304.

The control unit 303 selects the data addressed to its own node fromamong the received data stored in the memory 304, and sends this data tothe decoding unit 306 via the maximum likelihood processing unit 305.The maximum likelihood processing unit 305 estimates the most likelydata from among plural pieces of input data, and generates output data.The decoding unit 306 receives the most likely data from the maximumlikelihood processing unit 305, decodes the received data, and outputsAV data. The AV data output from the decoding unit 306 is used inprocessing such as video reproduction and display, audio reproduction,or the like.

Furthermore, the control unit 303 passes plural pieces of received datastored in the memory 304 to the wireless transmission unit 301 via themaximum likelihood processing unit 305; this received data is wirelesslytransmitted from the wireless transmission unit 301 in synchronizationwith the cycle timer 307. Further still, the control unit 303 passesterminal information of its own node to the wireless transmission unit301 as control data to be communicated to the control terminal 110; thisterminal information is wirelessly transmitted to the control terminal110. The terminal information is an individual ID (identifier) value setin advance for identification of the own node, capability information ofthe decoding unit 306, capability information of the wireless receivingunit 302 and wireless transmission unit 301, or the like.

The wireless transmission unit 301 and the wireless receiving unit 302of the node a 101 include DSSS type and OFDM type modulation units anddemodulation units. In the present embodiment, these two techniquesutilize techniques compliant with IEEE 802.11 and IEEE 802.11a, and thusdetailed descriptions thereof shall be omitted. The node a 101communicates using the OFDM type modulation unit when transmittingstream data and using the DSSS type modulation unit when transmittingother control data. In addition, the node a 101 communicates using theOFDM type demodulation unit when receiving stream data and using theDSSS type demodulation unit when receiving other control data, controlsignals, and so on. Detailed descriptions of the wireless transmissionunit 301 and the wireless receiving unit 302 shall be provided later.

(DSSS and OFDM Techniques)

Next, explanations shall be provided regarding the characteristicdifferences between the DSSS and OFDM techniques utilized in the presentembodiment.

The DSSS technique utilized by the control terminal 110 and the nodes a101 to i 109 is a modulation technique that directly spreads data withspread code using the Differential Binary Phase Shift Keying (DBPSK)modulation technique. This can be implemented by a simple circuit, andthus is a data communication technique capable of low-delay processing.While the transmission rate is a low 1 Mbps, the technique is highlyresistant to errors, and can properly transmit data over long distanceseven in communication environments having poor transmission conditions.

Additionally, the OFDM technique of the present embodiment utilizes anadvanced modulation technique called the 64-position QuadratureAmplitude Modulation (64QAM) technique. While this technique has aheavier processing load and higher delay than the stated DSSS technique,it is capable of realizing a high 54 Mbps bitrate. However, the errorresistance is low compared to the stated DSSS technique, and the signaltransmission range in which information can be properly transmitted issmaller than that of the DSSS technique.

FIG. 4 is a diagram schematically illustrating the difference in thesignal transmission range between the DSSS and OFDM techniques. In FIG.4, 401 schematically indicates the concept of the distance that data canbe properly transmitted using the OFDM technique, while 402schematically indicates the concept of the distance that data can beproperly transmitted using the DSSS technique. In other words, FIG. 4conceptually illustrates that the control terminal 110 and the nodes a101 to i 109 are capable of data communication at 1 Mbps using the DSSStechnique. Furthermore, FIG. 4 conceptually illustrates that the controlterminal 110 and the nodes a 101 to c 103 and e 105 are capable of datacommunication at 54 Mbps using the OFDM technique.

However, here, nodes outside of the transmission range 401 are alsocapable of data communication using the OFDM technique if errors of acertain degree can be overcome. The probability of an error occurringgenerally increases as the transmission distance increases. ForwardError Correction (FEC) code is added to the transmitted data frames forerror correction on the receiving side. Therefore, due to errorcorrection, it is possible to estimate the original data if thetransmission conditions are favorable and the degree of the error issmall, even if the node is outside of the transmission range 401; thuscorrect data reception is possible with communication using the OFDMtechnique.

Although the above descriptions discuss the case of the control terminal110 transmitting data, the same applies in the case where any of thenodes a 101 to i 109 transmit data using the OFDM technique. In otherwords, 54 Mbps communication using the OFDM technique is possiblebetween nearby nodes, and 1 Mbps communication using the DSSS techniqueis possible between faraway nodes, the control terminal, and so on.

(Wireless Transmission Unit/Wireless Receiving Unit of the ControlTerminal)

Next, the wireless transmission unit 201 and wireless receiving unit 202of the control terminal 110 shall be described with reference to FIG. 5.FIG. 5 is a diagram illustrating a detailed configuration of thewireless transmission unit 201 and wireless receiving unit 202 of thecontrol terminal 110.

501 is a scrambling unit for randomizing a bit string and reducing itscorrelation with an unrelated bit string; 502 is a modulation unit thatperforms DBPSK modulation; and 503 is a spreading unit that performsspectrum spreading using spread code. A DSSS type modulation unit 521 isconfigured of the scrambling unit 501, modulation unit 502, andspreading unit 503.

504 is a convolutional encoding unit that performs redundant encodingfor error correction processing. 505 is a modulation unit that dividesinput data among 48 subcarriers and performs 64 Quadrature AmplitudeModulation (QAM). 506 is an Inverse Fast Fourier Transform (IFFT) unitthat performs an inverse Fast Fourier Transform on each modulatedsubcarrier signal. 507 is a Guard Interval (GI) adding unit that adds aguard interval for canceling the influence of delay interference waves.508 is a shaping unit that performs waveform shaping in order to reduceout-of-band power. An OFDM type modulation unit 522 is configured of theconvolutional encoding unit 504, modulation unit 505, IFFT unit 506, GIadding unit 507, and shaping unit 508.

509 is a modulation unit that performs orthogonal modulation at anintermediate frequency. 510 is a multiplier that converts a signal inputfrom the modulation unit 509 into a wireless carrier frequency. 511 is apower amplifier (PA) that amplifies the wireless transmission power.

Only one of the DSSS type modulation unit 521 and the OFDM typemodulation unit 522 operates. In other words, the transmitted data isprocessed by either the scrambling unit 501 or the convolutionalencoding unit 504. The processed data is then output from either thespreading unit 503 or the shaping unit 508, and input into themodulation unit 509.

512 is an oscillator that generates an intermediate frequency, whereas513 is an oscillator that generates a wireless carrier frequency. 514 isa low noise amplifier (LNA) that amplifies a received signal. 515 is amultiplier that extracts a signal tuned by the wireless carrierfrequency. 516 is an automatic gain control (AGC) that automaticallyadjusts the signal strength to a predetermined amplitude strength. 517is a detection unit that converts the frequency of the signal to anintermediate frequency and performs quadrature detection.

518 is a despreading unit that multiplies the spread signal by spreadcode and produces the original signal. 519 is a demodulation unit thatgenerates the original data from the DBPSK-modulated signal. 520 is adescrambling processing unit that returns the scrambled data to itsoriginal state. The DSSS type demodulation unit 523 is configured of thedespreading unit 518, the demodulation unit 519, and the descramblingprocessing unit 520.

(Wireless Transmission Unit/Wireless Receiving Unit of the Nodes)

FIG. 6 is a diagram illustrating a detailed configuration of thewireless transmission unit 301 and wireless receiving unit 302 of thenode a 101. The same applies to nodes b 102 to i 109.

601 is a scrambling unit for randomizing a bit string and reducing itscorrelation with an unrelated bit string; 602 is a modulation unit thatperforms DBPSK modulation; and 603 is a spreading unit that performsspectrum spreading using spread code. A DSSS type modulation unit 629 isconfigured of the scrambling unit 601, modulation unit 602, andspreading unit 603.

604 is a convolutional encoding unit that performs redundant encodingfor error correction processing. 605 is a modulation unit that dividesinput data among 48 subcarriers and performs 64QAM modulation. 606 is anIFFT unit that performs an inverse Fast Fourier Transform on eachmodulated subcarrier signal. 607 is a GI adding unit that adds a guardinterval for canceling the influence of delay interference waves. 608 isa shaping unit that performs waveform shaping in order to reduceout-of-band power. An OFDM type modulation unit 630 is configured of theconvolutional encoding unit 604, modulation unit 605, IFFT unit 606, GIadding unit 607, and shaping unit 608. Additionally, the modulation unit605 and GI adding unit 607 perform symbol synchronization in accordancewith the synchronization signal from the wireless receiving unit 302.

609 is a modulation unit that performs orthogonal modulation at anintermediate frequency.

610 is a multiplier that converts a signal into a wireless carrierfrequency. 611 is a PA that amplifies the wireless transmission power.

Only one of the DSSS type modulation unit 629 and the OFDM typemodulation unit 630 operates. In other words, the transmitted data isprocessed by either the scrambling unit 601 or the convolutionalencoding unit 604. The processed data is then output from either thespreading unit 603 or the shaping unit 608, and input into themodulation unit 609.

612 is an oscillator that generates an intermediate frequency, whereas613 is an oscillator that generates a wireless carrier frequency. 614 isan LNA that amplifies a received signal. 615 is a multiplier thatextracts a signal tuned by the wireless carrier frequency. 616 is anautomatic gain control (AGC) that automatically adjusts the signalstrength to a predetermined amplitude strength. 617 is a detection unitthat converts the frequency of the signal to an intermediate frequencyand performs quadrature detection.

618 is a despreading unit that multiplies the spread signal by spreadcode and produces the original signal. 619 is a demodulation unit thatgenerates the original data from the DBPSK-modulated signal. 620 is adescrambling processing unit that returns the scrambled data to itsoriginal state. A DSSS type demodulation unit 632 is configured of thedespreading unit 618, the demodulation unit 619, and the descramblingprocessing unit 620.

621 is an automatic frequency control (AFC) unit that corrects errors inthe wireless carrier frequency. 622 is a GI removal unit that removesthe guard interval added at the time of transmission. 623 is a timingdetection unit that detects, from the received signal, thesynchronization timing between the frequency synchronization of thewireless carrier frequency, the frequency synchronization of theintermediate frequency, and the frequency symbol. 624 is a FFT unit thatperforms a Fast Fourier Transform for dividing the received data intoeach of the subcarriers. 625 is a channel estimation unit that estimatestransmission path distortion of the subcarrier signal, and 626 is anequalization unit that removes transmission path distortion from thereceived data in accordance with the estimation of the transmission pathdistortion. In other words, the processing performed by the channelestimation unit 625 and equalization unit 626 is maximum likelihoodprocessing that estimates the original data from the received dataincluding a multipath signal and the like. 627 is a demodulation unitthat restores the original data per subcarrier. 628 is a phase detectioncorrection unit that detects the phase of each subcarrier and generatesa correction signal, and 641 is a Viterbi decoding unit that performserror correction on the convolutionally encoded data and restores theoriginal data. An OFDM type decoding unit 631 is configured of thestated functional processing units from the AFC unit 621 to the Viterbidecoding unit 641.

The timing detection unit 623 and the phase detection correction unit628 synchronize a detected timing with the synchronization cycle of theoverall system, and hold that synchronization; the timing detection unit623 and the phase detection correction unit 628 operate spontaneouslyeven during periods where there is no received data, and continue togenerate a cyclical synchronization signal. By providing thesynchronization signal to the modulation unit 605 and the GI adding unit607 of the wireless transmission unit 301, the operations of thewireless transmission unit 301 and the wireless receiving unit 302 aresynchronized. In other words, operations are carried out so that thesynchronization timing of the own node is synchronized with thesynchronization timing of the received data, and the data is transmittedin accordance with that synchronization timing. In this manner, nodesoperate in synchronization with one another, and thus synchronization ofthe entire communication network, in which nodes are communicating withone another, is established.

(Control Terminal Operations)

Next, operations of the control terminal 110 shall be described withreference to FIGS. 7, 8A, and 8B. FIG. 7 is a flowchart illustrating anoperational procedure performed by the control terminal 110. FIGS. 8Aand 8B are time slot diagrams illustrating operations of the controlterminal 110.

In FIG. 7, first, the control terminal detects the plural nodes presentin the surrounding area, and furthermore performs processing fordetermining the node topology (Step S1) in order to determine thepositional relationships between the nodes. Details of the node topologydetermination processing shall be provided later.

Next, in accordance with the determined node topology, or in otherwords, in accordance with the relative positions of the nodes, thetimeslot configuration and node group allocation for synchronizedcommunication is determined, and the resultant is communicated to allnodes by the wireless transmission unit 201 using the DSSS technique(Step S2). In the case of the present embodiment, the nodes a 101 to i109, as shown in FIG. 1, are detected. Then, in accordance with thepositional relationship between the nodes and the control terminal 110,the nodes are divided into groups 1 (112), 2 (113), and 3 (114), fromthe nearer nodes outward. Next, the timeslots are allocated as indicatedby FIG. 8A. 801 is a time interval Tf of the repeat cycle ofsynchronized transfer. 802 is a shared slot, slot 0, capable of beingused in common by the control terminal 110 and the nodes, and the timeinterval thereof is Tc. 803 is a slot, slot 1, capable of transmissionby the control terminal 110. 804 is a slot, slot 2, capable oftransmission by the nodes of group 1 (112). 805 is a slot, slot 3,capable of transmission by the nodes of group 2 (113). 806 is a slot,slot 4, capable of transmission by the nodes of group 3 (114). The timeintervals for slots 1 to 4 are each the same Ts.

Next, the cycle timer 206 starts timer operations at the cycle Tf of thetime division communication in accordance with the stated time slotconfiguration (Step S3). When the cycle timer 206 reaches the startingtime of the synchronization cycle Tf (YES in Step S4), the proceduremoves to Step S5.

In Step S5, the control terminal 110 transmits beacon signals fornotifying all nodes of the synchronization timing, as indicated by 807to 810 in FIG. 8A. These beacon signals (807, 808, 809, and 810) aretransmitted from the wireless transmission unit 201 using the DSSStechnique, which is capable of long-distance communication.

Next, the control terminal 110 determines whether or not control data tobe transmitted through the shared slot, slot 0 (802), is present (StepS6). In the case where such control data is present (YES is Step S6),the procedure moves to Step S7, and the control data to be transmittedis transmitted from the wireless transmission unit 201 using the DSSStechnique at the timing of slot 0 (802) indicated by the cycle timer206. The procedure then moves to Step S8. In the case where the controldata is not present (NO in Step S6), the procedure moves to Step S8.

Furthermore, the control terminal 110 determines whether or not controldata to be received at the timing of the shared slot, slot 0 (802), asindicated by the cycle timer 206, is present (Step S8). In the casewhere control data to be received is present (YES in Step S8), theprocedure moves to Step S9, and the control data is received by thewireless receiving unit 202 using the DSSS technique. The procedure thenmoves to Step S10. In the case where control data to be received is notpresent (NO in Step S8), the procedure moves to Step S10.

Next, the control terminal 110 determines whether or not stream data tobe transmitted is present (Step S10). In the case where such stream datais present (YES in Step S10), the procedure moves to Step S11, whereasin the case where such stream data is not present (NO in Step S10), theprocedure returns to Step S4 and the process repeats.

In Step S11, transmission is performed from the wireless transmissionunit 201 using the OFDM technique, at the timing of the slot 1 (803)indicated by the cycle timer 206, the slot 1 being a slot usable by thecontrol terminal. The stream data frame transmitted at this time isindicated by 815 in FIG. 8B. The stream data frame 815 is configured ofstream data D1 (816) to D9 (824) addressed to the respective nodes.

D1 (816), which makes up part of the stream data frame, is stream dataaddressed to the node a 101. Additionally, D2 (817) is stream dataaddressed to the node b 102. D3 (818) is stream data addressed to thenode c 103. In the same manner, D4 (819) to D9 (824) are pieces ofstream data addressed to the nodes d 104 to i 109 respectively. Theframe configuration of the transmitted stream data frame 815 iscommunicated in advance to all nodes in Step S2. Therefore, each nodecan identify the data portion addressed to itself from among thereceived stream data frame 815.

When the stream data frame is transmitted in Step S11 in this manner,the control terminal 110 once again returns to Step S4, waits until thestarting time of the next synchronization cycle Tf, and repeats theabovementioned operations.

Therefore, the control terminal 110 transmits the beacon signals (811,812, 813, and 814) per cycle Tf, and transmits the stream data frames(815, 825, 826) through slot 1 (803) per cycle Tf. FIG. 8B illustratesthe transmission operations of the control terminal 110 performed atthis time.

(Node Operations)

Next, the operations of the nodes shall be described with reference toFIG. 9. FIG. 9 is a flowchart illustrating a processing procedureperformed by each node. Note that the descriptions explicitly providedhere discuss the case of the operations of the node a 101 as an example;however, the nodes b 102 to i 109 also operate with the same procedure.

First, a single or plural nodes present in the area surrounding the nodea 101 are detected, and inter-node information necessary for the controlterminal 110 to perform the processing for determining the node topologyis transmitted to the control terminal 110 (Step S21). The processingfor detecting the surrounding nodes performed by the control terminal110 shall be described later in detail in the descriptions of theprocessing for determining the node topology.

Next, control data transmitted from the control terminal 110, includinginformation of the synchronized communication timeslot configuration andthe node group allocation, is received by the wireless receiving unit302 using the DSSS technique (Step S22). Node a (101) acquires thetimeslot configuration in accordance with the received control data,identifies the frame configuration of the stream data frame 815, andidentifies the layout of the data D1 (816) addressed to itself. Inaddition, the node a (101) acquires information of the group to which itbelongs, in accordance with the received control data, and identifiesthe slot through which it performs transmission.

Next, the node a (101) determines whether or not a beacon signal hasbeen received (Step S23), and in the case where a beacon signal has beenreceived (YES in Step S23), the procedure moves to Step S24, whereas inthe case where a beacon signal has not been received (NO in Step S23),the procedure moves to Step S26. In Step S24, the cycle timer isrestarted. Through this restarting process (Step S24), the cycle timer206 of the control terminal 110 and the cycle timer 307 of the node a(101) are synchronized, and determination of the cycle Tf and slots 0 to4 becomes possible on the node side.

Next, the node a (101) extracts plural pieces of stream data D1addressed to itself from among the plural stream data frames stored inthe memory 304, and sends the stream data D1 to the maximum likelihoodprocessing unit 305; the data on which maximum likelihood processing hasbeen performed is sent to the decoding unit 306 and decoded into AV data(Step S25). However, when there is only a single piece of stream data D1in the memory 304, the maximum likelihood processing is bypassed, andthe stream data D1 is sent to the decoding unit 306. Additionally,storage of the received stream data within the memory 304 occurs in StepS27, which shall be described later.

Next, the node a 101 determines whether or not the wireless receivingunit 302 is receiving stream data (Step S26). In the case wherereceiving is being carried out (YES in Step S26), the procedure moves toStep S27, whereas in the case where receiving is not being carried out(NO in Step S26), the procedure moves to Step S28. In Step S27, thestream data frame is received by the wireless receiving unit 302 usingthe OFDM technique, and is stored in the memory 304. Here, the node a101 has, within a single Tf cycle, three receiving slots, or the slots 1(803), 3 (805), and 4 (806), which are slots aside from the node a 101'sown transmission slot. Therefore, although processing for storing thestream data frame occurs three times within a single Tf cycle, these arestored independently in the memory 304 and are used in the maximumlikelihood processing of the aforementioned Step S25.

Next, it is determined whether or not the time indicated by the cycletimer 307 is the transmission slot of the node itself (Step S28). Thetransmission slot is slot 2 if the node is in group 1 (112), slot 3 ifthe node is in group 2 (113), and slot 4 if the node is in group 3(114). Then, if the current time is the starting timing of thetransmission slot (YES in Step S28), the procedure moves to Step S29,whereas in other cases (NO in Step S28), the procedure returns to StepS23.

In Step S29, it is determined whether or not the group to which the nodeitself belongs is group 1 (112). To rephrase, in Step S29, it isdetermined whether a stream data frame is being received a plurality oftimes at the starting time of the transmission slot of the node itself.In the case where the node belongs to group 1, the stream data frame isreceived directly from the control terminal 110; thus, the same data isnot being received a plurality of times, and the maximum likelihoodprocessing is therefore unnecessary. As opposed to this, in the casewhere the node does not belong to group 1, the same data is received aplurality of times from plural nodes, and therefore it is necessary tocarry out the maximum likelihood processing. In the case where the nodehas been determined not to belong to group 1 (112) (NO in Step S29), theprocedure moves to Step S30, whereas in the case where the node has beendetermined to belong to group 1 (112) (YES in Step S29), the proceduremoves to Step S31.

In Step S30, the stream data frames within the memory 304 are sent tothe maximum likelihood processing unit 305, and the stream data frameobtained by performing the maximum likelihood processing is transmittedfrom the wireless transmission unit 301 using the OFDM technique. Thestream data frame transmitted at this time is a frame in which thestream data D1 (816) to D9 (824) of all nodes are included. On the otherhand, in Step S31, one of the stream data frames within the memory 304and received from the control terminal 110 is transmitted as-is from thewireless transmission unit 301 using the OFDM technique.

In the manner described thus far, upon transmitting the stream data inStep S30 or Step S31, the node a 101 once again returns to Step S23, andthe abovementioned processing is repeated. Accordingly, each noderepeats the following process within a Tf cycle: receiving stream data aplurality of times; performing maximum likelihood processing on anddecoding the data addressed to itself from among the received data; andperforming maximum likelihood processing on and transmitting thereceived stream data.

(Cooperative Operations Between Control Terminal and Node)

FIGS. 10A, 10B, 10C, 10D, and 11 illustrate the operations of thecontrol terminal 110 and the nodes 101 to 109 as described above. FIGS.10A, 10B, 10C, and 10D are diagrams conceptually illustrating the changeover time of the transmission of stream data by the control terminal 110and the nodes. FIG. 11 is a diagram illustrating transmission of streamdata by the control terminal 110 and nodes on the time axis.

First, in the time of slot 1 (803) shown in FIG. 11, the controlterminal 110 transmits a stream data frame, as shown in FIG. 10A. Atthis time, the signal that reaches the nearby nodes a 101, b 102, and c103 is strong, and thus the stream data frame can be received with a lowrate of error. However, as the position of the node grows more distant,the signal that reaches that node grows weaker, and thus distant nodesreceive the stream data frame with a high rate of error. The stream dataframe transmitted by the control terminal 110 at this time is the dataframe indicated by 815 in FIG. 11. As shown in FIG. 8B, the data frame815 includes data addressed to all of the nodes a 101 to i 109.

Next, in the time of slot 2 (804), the nodes a 101 to c 103 of group 1(112) transmit stream data frames, as shown in FIG. 10B. At this time,the signal that reaches the nearby nodes d 104 to f 106 is strong, andthus the stream data frames can be received with a low rate of error.However, as the position of the node grows more distant, the signal thatreaches that node grows weaker, and thus distant nodes receive thestream data frames with a high rate of error. The stream data framestransmitted by the nodes a 101 to c 103 at this time are the frame dataindicated by 901 to 903 in FIG. 11. In other words, the nodes a 101, b102, and c 103 transmit the data frames they received in slot 1 (803)as-is, and therefore the same data is transmitted from three pointssimultaneously. When the same data is transmitted simultaneously fromplural points, it can be handled in the same way as a multipath wave, asfar as the receiving nodes are concerned; accordingly, maximumlikelihood processing and estimation of the original data can beperformed by the channel estimation unit 625 and the equalization unit626 of the wireless receiving unit 302 in each node.

Next, in the time of slot 3 (805), the nodes d 104 to f 106 of group 2(113) transmit stream data frames, as shown in FIG. 10C. At this time,the signal that reaches the nearby nodes a 101 to c 103 and g 107 to i109 is strong, and thus the stream data frames can be received with alow rate of error. However, as the position of the node grows moredistant, the signal that reaches that node grows weaker, and thusdistant nodes receive the stream data frames with a high rate of error.The stream data frames transmitted by the nodes d 104 to f 106 at thistime are the frame data indicated by 904 to 906 in FIG. 11. In otherwords, the nodes d 104 to f 106 perform maximum likelihood processing onthe data frames received in slot 1 (803) and slot 2 (804) and transmitthe data frames, and therefore the same data is transmitted from threepoints simultaneously. When the same data is transmitted simultaneouslyfrom plural points, it can be handled in the same way as a multipathwave, as far as the receiving nodes are concerned; accordingly, maximumlikelihood processing and estimation of the original data can beperformed by the channel estimation unit 625 and the equalization unit626 of the wireless receiving unit 302 in each node.

Lastly, in the time of slot 4 (806), the nodes g 107 to i 109 of group 3(114) transmit stream data frames, as shown in FIG. 10D. At this time,the signal that reaches the nearby nodes d 104 to f 106 is strong, andthus the stream data frames can be received with a low rate of error.However, as the position of the node grows more distant, the signal thatreaches that node grows weaker, and thus the stream data frames arereceived with a high rate of error. The stream data frames transmittedby the nodes g 107 to i 109 at this time are the frame data indicated by907 to 909 in FIG. 11. In other words, the nodes g 107 to i 109 performmaximum likelihood processing on the data frames received in slot 1(803), slot 2 (804), and slot 3 (805), and transmit the data frames, andtherefore the same data is transmitted from three points simultaneously.When the same data is transmitted simultaneously from plural points, itcan be handled in the same way as a multipath wave, as far as thereceiving nodes are concerned; accordingly, maximum likelihoodprocessing and estimation of the original data can be performed by thechannel estimation unit 625 and the equalization unit 626 of thewireless receiving unit 302 in each node.

Through the stated process, within the repeating cycle Tf, each nodereceives the same stream data frames from plural nodes and stores thestream data frames in the memory 304. Then, upon receiving the nextbeacon signal 812, each node extracts plural pieces of data addressed tothe node itself from the plural stream data frames stored in the memory304, performs maximum likelihood processing through the maximumlikelihood processing unit 305, and reproduces the original data. Thereproduced data is sent to the decoding unit 306.

(Node Topology Determination Processing)

Next, node topology determination processing executed by the controlterminal 110 in Step S1 of FIG. 7 shall be described using FIG. 12. FIG.12 is a diagram illustrating procedures for node topology determinationprocessing performed by the control terminal and by the nodes. Note thatthe control terminal 110 and the nodes use the DSSS technique whentransmitting/receiving wireless signals in this node topologydetermination process.

First, the control terminal 110 carries out processing for recognizingnodes present in the surrounding area (Step S41). Recognizing nodes isperformed through a repeating procedure, in which the control terminal110 broadcasts an inquiry signal, and the nodes that receive the inquirysignal add an individual ID value, provided individually to each node inadvance, to a response signal and broadcast the response signal. Thenodes randomly change the transmission timing of the response signalwithin a range up to a maximum wait time Tmax so as to avoid havingtheir response signals interfere with the response signals from othernodes. The control terminal 110 repeatedly transmits the inquiry signaluntil response signals cease to arrive within the maximum waiting timeTmax, thereby receiving a response signal from all of the nodes. In thismanner, the control terminal 110 acquires the individual ID values ofall nodes present in the surrounding area.

Next, the control terminal 110 allocates node numbers, corresponding tothe individual ID numbers, to all the recognized nodes, and notifies thenodes of these node numbers (Step S42). Numbers such as node 1, node 2,and node 3, . . . , node 9 are dealt to each node a˜i in this manner.

Next, the control terminal 110 instructs all nodes to begin measuringthe signal strength of a training signal (Step S43). All nodes thatreceive this instruction move to a status in which they measure thesignal strength of the training signals transmitted in order from theother nodes, including the control terminal, and create measurementresult lists (Step S50).

Then, first, the control terminal 110 commences transmission of thetraining signal (Step S44). Note that this training signal has a presettransmission power strength, and is transmitted at the same signalstrength from the control terminal 110 and all the nodes.

Next, the control terminal 110 sequentially requests each node totransmit a training signal of a preset transmission power strength (StepS45). That is, the control terminal 110 selects each node sequentially,and requests the select node to transmit the training signal. The nodesthat receive the request instruction transmit the training signals(Steps S51, S52, and S53). During this time, the control terminal 110measures the signal strengths of the training signals transmitted byeach node (Step S46). Here, as described above, each node is performingthe measurement processing of the signal strength of the trainingsignals (Step S50) on receiving the instruction from the controlterminal 110 at step S43. When the transmission of the training signalhas finished for all nodes, the control terminal 110 then inquires toeach node and receives the measurement result list from each node (StepS47).

The received signal strength of the training signals received by thecontrol terminal 110 and the nodes is inversely proportional to thedistance between nodes, as illustrated in FIG. 13. FIG. 13 is a diagramschematically illustrating a relationship between the strength of areceived training signal and the distance between nodes. Accordingly,the control terminal 110 is provided with a list in which thecorresponding relationship between the received signal strengths and thedistances is pre-measured, and from this measurement result list,determines the distance between the nodes. If the distance between thenodes can be determined, it is possible to estimate the positionalrelationship between each of the nodes using a publicly knowntriangulation method such as that illustrated in FIG. 14 (Step S48).FIG. 14 is a diagram schematically illustrating the estimation of apositional relationship through the triangulation method. The distancebetween the control terminal 110 and the nodes (for example, thedistance between the control terminal and the nodes a and b) can beestimated based on the training signal received in Step S46. Inaddition, the distance between nodes (for example, the distance betweenthe nodes a and b) can be estimated based on the measurement resultsreceived in Step S47 (for example, the measurement results from nodes aand b).

The control terminal 110 first determines the length of the necessarystream data frame 815 based on the total number of nodes, and thendetermines the beacon cycle Tf 801 based on the bitrate of the streamdata frame. The control terminal 110 then determines the number of groupdivisions based on the beacon cycle Tf, the data frame length, and thetotal number of nodes. In this manner, the time slot configuration suchas that shown in FIGS. 8A and 8B is determined; adjacent nodespositioned close to the control terminal 110 are configured into thesame group based on the positional relationships between the nodes; andthe layout map shown in FIG. 1 is created. Then, in accordance with thelayout map, the groups to which the nodes belong and the time slotconfiguration are determined, and the determination is communicated tothe nodes (Step S49).

In the configuration according to the present embodiment as describedthus far, plural communication terminals make up a synchronized-typenetwork; within each synchronization cycle, plural transmissionterminals transmit data of a predetermined length, and receivingterminals perform maximum likelihood processing on the plural pieces ofreceived data and finalize the received data. Thus, according to theconfiguration of the present embodiment, plural communication devicesredundantly transmit the same data within the same cycle; therefore, anabnormality arising in a single communication connection is solvedthrough the other communication connections, and the data can betransmitted to all of the communication devices within the same cycle.Additionally, all of the terminals are temporally synchronized, whichmakes it possible to avoid transmissions from interfering with oneanother. Accordingly, it is possible to realize communication in whichdata disconnections and interruptions do not occur, even when handlingstream data that is temporally continuous, such as video or audio. It isalso possible to carry out communication in which plural transmissionterminals simultaneously transmit plural data streams withoutinterfering with one another.

Embodiment 2

In the previously described embodiment, nodes belonging to the finalgroup also transmit stream data frames. However, in order to effectivelyutilize the communication bandwidth, the nodes of the final group mayoperate so as not to carry out transmission when the redundancy of thereceived data of each of the nodes is ensured. For example, in the casewhere the number of groups is three, as in the first embodiment, slot 4becomes unnecessary, and thus it is possible to reduce the bandwidthused by all nodes within the repeating cycle Tf by omittingcommunication through slot 4.

Under these conditions, the method of allocating the time slots inaccordance with the number of groups may be performed as follows.Descriptions shall first be provided regarding the case where there is asingle group. In this case, as illustrated in FIG. 15, all nodes receivedata directly from the control terminal, and thus the nodes in group 1(112) do not need to transmit the received data further on. FIG. 15 is adiagram schematically illustrating a configuration of a network whenthere is a single group. Therefore, the only timeslots required are twoslots, or the shared slot, slot 0, and the transmission slot, slot 1. Inthis case, the redundancy in each node is only 1; however, because thedata transmitted from the control terminal 110 is the most correct data,a higher redundancy is not necessary. If a node within the group has apoor reception state, that node may be separated into a differencegroup.

Next, descriptions shall be provided regarding the case where there aretwo groups. In this case, when the nodes of group 2, which is the finalgroup, do not carry out transmission, the data path through which thenodes carry out reception is as illustrated in FIG. 16. FIG. 16 is adiagram schematically illustrating a configuration of a network whenthere are two groups. The nodes in group 1 (112) only receive thetransmission data from the control terminal 110, and thus the redundancythereof is 1. The nodes in group 2 (113) receive the transmission datafrom the control terminal 110 and the transmission data from the nodesof group 1 (112), and thus the redundancy thereof is 2. Therefore, ifthe nodes of group 2 (113) carry out transmission further on, theredundancy of the nodes in group 1 (112) can be set at 2. At firstglance, having group 1 (112) receive the transmission data of group 2(113) appears to be meaningless. However, for example, due to thetransmission performed by group 2 (113), the node a 101 receives data ona direct path from the control terminal 110, and furthermore receivesthe data sent on a path from the control terminal 110 via the node c 103and the node e 105. Accordingly, it is possible to set the redundancywith data received from differing paths at 2, making it possible toexpect a reduction in errors through the maximum likelihood processing.

Detailed descriptions of the process for determining groups andtimeslots (Step S49 in FIG. 12) performed by the control terminal 110,which carries out the above-described operations, shall be provided withreference to FIG. 17. FIG. 17 is a flowchart illustrating a procedurefor processing performed by the control terminal 110 to determine groupsand time slots in the present embodiment.

First, the control terminal 110 finalizes the layout and number of allnodes, in the same manner as the process from Step S41 to Step S48 inthe aforementioned first embodiment (Step S61). Then, the controlterminal 110 determines the length of the necessary stream data frame815 based on the total number of nodes, and then determines the beaconcycle Tf (801) based on the bitrate of the stream data frame (Step S62).The control terminal 110 then determines the number of group divisions Nbased on the beacon cycle Tf, the data frame length, and the totalnumber of nodes (Step S63).

Next, in the case where the number of group divisions N is 1 (YES inStep S64), the number of slots into which the cycle Tf is divided is setto N+1 (Step S65). In other words, the cycle Tf is divided by two slots:slot 0, which is the shared slot, and slot 1, which is the transmissionslot of the control terminal 110. The procedure then moves to Step S70.

Next, in the case where the number of group divisions N is 2 (YES inStep S66), the number of slots into which the cycle Tf is divided is setto N+2 (Step S67). In other words, the cycle Tf is divided by fourslots: slot 0, which is the shared slot; slot 1, which is thetransmission slot of the control terminal 110; slot 2, which is thetransmission slot of group 1; and slot 3, which is the transmission slotof group 2. The procedure then moves to Step S70.

In the case where the number of group divisions N is three or more (YESin Step S68), the number of slots into which the cycle Tf is divided isset to N+1 (Step S69). In other words, the cycle Tf is divided by N+1slots: slot 0, which is the shared slot; slot 1, which is thetransmission slot of the control terminal 110; and slots 2 to N, whichare the transmission slots of groups 1 to (N−1). The procedure thenmoves to Step S70.

In this manner, the time slot configuration such is determined inaccordance with the number of group divisions N; adjacent nodespositioned close to the control terminal 110 are configured into thesame group based on the positional relationships between the nodes; anda layout map identical to that shown in FIG. 1 is created. Then, in StepS70, in accordance with the layout map, the groups to which the nodesbelong and the time slot configuration are determined, and thedetermination is communicated to the nodes.

As described thus far, according to the configuration of the presentembodiment, groups that do not need to transmit data further on, such asthe final group to receive the data within each time interval of therepeating cycle, do not carry out communication. For this reason,according to the configuration of the present embodiment, it is possibleto allocate the groups necessary for communication to a longer timeinterval, and thus it is possible to increase the speed of datatransfer.

Embodiment 3

In the first and second embodiments, the beacon signal is used only as asignal that communicates the timing of the repeating cycle Tf. However,by adding control information to this beacon signal, the controlterminal 110 may communicate the timings of each of the slots, specifythe node that uses the shared slot, and so on.

FIG. 18 is a diagram illustrating transmission of stream data by thecontrol terminal 110 and nodes on the time axis in the case wherecontrol information has been added to the beacon signal. In FIG. 18, 921is the repeating cycle Tf, 922 is the shared slot, slot 0, and 923 isthe transmission slot, slot 1, of the control terminal 110. 924 to 926are transmission slots, slots 2 to 4, of groups 1 to 3 respectively. 927to 932 are beacon signals to which control information has been added.933 is a stream data frame transmitted by the control terminal 110,whereas 934 to 942 are stream data frames transmitted by the nodes a 101to i 109 respectively.

Information indicating the start of the cycle Tf and informationindicating that node a 101 is permitted to use the shared slot, slot 0,is added to the beacon signal indicated by 927. If, at this time, node a101 has information to be communicated to the control terminal 110, nodea 101 transmits control data. When node a 101 does not have informationto be communicated, node a 101 simply stands by for reception. Nodes b102 to i 109 also simply stand by for reception.

Information indicating that authority to transmit stream data frames hasbeen given to the control terminal 110 is added to the beacon signalindicated by 928. In response to the beacon signal 928, the controlterminal 110 transmits the stream data frame 933.

Information indicating that authority to transmit stream data frames hasbeen given to group 1 is added to the beacon signal indicated by 929.The nodes a 101 to c 103, which receive the beacon signal 929, transmitthe stream data frames 934 to 936.

Information indicating that authority to transmit stream data frames hasbeen given to group 2 is added to the beacon signal indicated by 930.The nodes d 104 to f 106, which receive the beacon signal 930, transmitthe stream data frames 937 to 939.

Information indicating that authority to transmit stream data frames hasbeen given to group 3 is added to the beacon signal indicated by 931.The nodes g 107 to i 109, which receive the beacon signal 931, transmitthe stream data frames 940 to 942.

Lastly, information indicating the start of the cycle Tf and informationindicating that node b 102 is permitted to use the shared slot, slot 0,is added to the beacon signal indicated by 932.

Information of the control terminal 110, node a 101, node b 102, node c103, and on up to node i 109 is specified repeatedly in sequence, asinformation of terminals permitted to carry out transmission, in thebeacon signal sent at the beginning of the cycle Tf.

In this manner, it is easier to achieve synchronization between nodes byhaving the starting timing of each slot be communicated by the beaconsignal. Additionally, the number of the node permitted to performtransmission may be specified rather than the group number that is addedto the beacon signal. Doing so makes it acceptable to carry outtransmission of the received data in accordance with the node numberspecified in the beacon signal, even if each node is not aware of thegroup to which it belongs. Accordingly, it is possible to simplify theoperational processing of the nodes.

Embodiment 4

In the first embodiment, maximum likelihood processing is performed ondata transmitted simultaneously from plural nodes in the same manner aswith multipath communication by the estimation unit 625 and theequalization unit 626, and the original data is estimated. However, OFDMsubchannels may be divided/allocated per transmission node, the data maybe stored as individual data in the memories 304 of the nodes on thereceiving side, and maximum likelihood processing may be performed bythe maximum likelihood processing unit 305.

In this case, for example, the OFDM technique in the present embodimentdivided communication into 48 subchannels, and the channels can beallocated for use by the nodes as follows:

channels 1 to 16: node a 101, node d 104, and node g 107;

channels 17 to 32: node b 102, node e 105, and node h 108;

channels 33 to 48: node c 103, node f 106, and node 109.

In this case, regarding the transmission data sent from the controlterminal 110, the same data is transmitted redundantly over channels 1to 16, 17 to 32, and 33 to 48, respectively.

By using such a configuration, it is possible for each node todistinguish transmission nodes and receive the data; thus it is possibleto more accurately restore the original data through the maximumlikelihood processing.

Embodiment 5

In the above embodiments, descriptions are given assuming an example inwhich the wireless scheme used by the wireless transmission units 201and 301 and the wireless receiving units 202 and 302 is the TimeDivision Multiple Access (TDMA) technique. However, the wireless schemeused is not limited thereto. For example, the Code Division MultipleAccess (CDMA) technique may be used. In this case, different spread codeis allocated per node that performs transmission at the same time asanother node, and the wireless transmission units modulate thetransmission data using the CDMA technique with the spread codeallocated to their own nodes, and transmit the data. On the other hand,the wireless receiving units are provided with plural spread codecorrelation devices; by performing plural correlations on receivedsignals, signals transmitted simultaneously from plural nodes are eachdivided, received, and stored in the memories. Then, maximum likelihoodprocessing is performed on the respective pieces of received data andthe original data is estimated.

Alternatively, the wireless scheme used by the wireless transmissionunits 201 and 301 and the wireless receiving units 202 and 302 may bethe Frequency Division Multiple Access (FDMA) technique. In this case,transmission frequencies are allocated per node that simultaneouslyperforms transmission. The wireless receiving units are provided withplural receiving units in parallel; data received simultaneously inparallel may be stored in the memories per frequency, maximum likelihoodprocessing performed on the received data within the memories, and theoriginal data estimated.

Alternatively, the space-division multiple access technique may be used.Or, a combination of the abovementioned communication techniques may beused.

In this manner, by using wireless techniques as necessary, it ispossible to carry out communication appropriate for the applications andgoals of the communication.

Embodiment 6

In the stated embodiments, the layout of the nodes is determined usingthe received signal strength of the wireless signal (the strength of thesignal transmitted from the nodes); however, the layout may bedetermined using an optical device, an acoustic device, or a differentkind of measurement device, or, alternatively, a combination of these.

For example, in the case of using an optical device (an optical imagingdevice), the control terminal is provided with a camera and a rangefinding unit for autofocus; the nodes are identified from an imagecaptured by the camera, and the distance to each node is measured by therange finding unit. Through this, the control terminal can determine thelayout of the nodes.

Or, for example, in the case of using an acoustic device, the controlterminal and the nodes can be provided with a speaker for outputtingsound waves (an acoustic signal) or ultrasonic waves (an ultrasonicsignal) and a microphone for detecting those waves. In this case, nodesare synchronized to one another; sound waves or ultrasonic waves areoutput by the nodes in order in synchronization with a reference time;the distance between the nodes is measured based on the amount of delaytime before the sound wave reaches the node (the transmission delay);and thereby, the control terminal can determine the layout of the nodes.Alternatively, because ultrasonic waves have strong directivity, adevice that structurally scans the space may be provided; the layout ofthe nodes is detected by measuring the delay of a reflected ultrasonicwave, using publicly known sonar technology, and the control terminalmay determine the node layout thereby.

Furthermore, a publicly known Global Positioning System (GPS) unit maybe provided in each node; each node autonomously detects its ownposition and communicates this to the control terminal, and the controlterminal may determine the node layout thereby.

In this manner, the layout of the nodes can be accurately detected byusing an optical device, an acoustic device, or a different kind ofmeasurement device, or, alternatively, a combination of these.

Embodiment 7

Although an embodiment of the present invention has been described indetail above, it is possible for the invention to take on the form of asystem, apparatus, program or storage medium. More specifically, thepresent invention may be applied to a system comprising a plurality ofdevices or to an apparatus comprising a single device.

It should be noted that there are cases where the object of theinvention is attained also by supplying a program, which implements thefunctions of the foregoing embodiments, directly or remotely to a systemor apparatus, reading the supplied program codes with a computer of thesystem or apparatus, and then executing the program codes.

Accordingly, since the functions of the present invention areimplemented by computer, the program codes per se installed in thecomputer also fall within the technical scope of the present invention.In other words, the present invention also covers the computer programitself that is for the purpose of implementing the functions of thepresent invention.

In this case, so long as the system or apparatus has the functions ofthe program, the form of the program, for example, object code, aprogram executed by an interpreter or script data supplied to anoperating system, etc., does not matter.

Examples of storage media that can be used for supplying the program area floppy (registered trademark) disk, hard disk, optical disk,magneto-optical disk, CD-ROM, CD-R, CD-RW, magnetic tape, non-volatiletype memory card, ROM, DVD (DVD-ROM, DVD-R), etc.

As for the method of supplying the program, a client computer can beconnected to a website on the Internet using a browser possessed by theclient computer, and the computer program per se of the presentinvention or a compressed file that contains an automatic installationfunction can be downloaded to a recording medium such as a hard disk.Further, the program of the present invention can be supplied bydividing the program code constituting the program into a plurality offiles and downloading the files from different websites. In other words,a WWW server that downloads, to multiple users, the program files thatimplement the functions of the present invention by computer also iscovered by the present invention.

Further, it is also possible to encrypt and store the program of thepresent invention on a storage medium such as a CD-ROM, distribute thestorage medium to users, allow users who meet certain requirements todownload decryption key information from a website via the Internet, andallow these users to run the encrypted program by using the keyinformation, whereby the program is installed in the user's computer.Further, besides the case where the aforesaid functions according to theembodiment are implemented by executing the read program by computer, anoperating system or the like running on the computer may perform all ora part of the actual processing so that the functions of the foregoingembodiment can be implemented by this processing.

Furthermore, after the program read from the storage medium is writtento a memory provided in a function expansion board inserted into thecomputer or a function expansion unit connected to the computer, a CPUor the like mounted on the function expansion board or functionexpansion unit performs all or a part of the actual processing so thatthe functions of the foregoing embodiment can be implemented by thisprocessing.

In this manner, according to the abovementioned embodiments, it ispossible to provide a technique for reducing the occurrence ofdisconnections or interruptions when transmitting/receiving stream datathat is temporally continuous, such as video or audio. It is furthermorepossible to provide a technique for avoiding mutual interference evenwhen simultaneously sending plural pieces of data to plural receivingterminals.

While the present invention has been described with reference toexemplary embodiments, it is to be understood that the invention is notlimited to the disclosed exemplary embodiments. The scope of thefollowing claims is to be accorded the broadest interpretation so as toencompass all such modifications and equivalent structures andfunctions.

This application claims the benefit of Japanese Patent Application No.2006-312132, filed Nov. 17, 2006, which is hereby incorporated byreference herein in its entirety.

What is claimed is:
 1. A control apparatus that performs communicationwith a plurality of communication apparatuses including a firstcommunication apparatus, a second communication apparatus, and a thirdcommunication apparatus, the control apparatus comprising: an allocationunit configured to allocate: a first communication slot for the first,second, and third communication apparatuses to receive first datadirectly transmitted from a data source, a second communication slot forthe second and third communication apparatuses to receive second datatransmitted from the first communication apparatus, the second databeing obtained by performing a relay transmission of the first data inthe first communication apparatus, and a third communication slot forthe third communication apparatus to receive third data transmitted fromthe second communication apparatus, the data being obtained byperforming maximum likelihood processing based on the first datatransmitted from the data source in the first communication slot, thesecond data transmitted from the first communication apparatus in thesecond communication slot, and the third data transmitted from thesecond communication apparatus in the third communication slot; and anotification unit configured to notify at least the first, the second,and the third communication apparatuses of the communication slotsallocated by the allocation unit.
 2. The control apparatus according toclaim 1, further comprising: a determination unit configured todetermine a relative position of each communication apparatus of theplurality of communication apparatuses, wherein the allocation unitallocates communication slots based on the relative position of eachcommunication apparatus of the plurality of communication apparatuses asdetermined by the determination unit.
 3. The control apparatus accordingto claim 1, wherein the allocation unit allocates communication slots inorder from a communication apparatus positioned nearest to the controlapparatus to a communication apparatus positioned farthest from thecontrol apparatus.
 4. The control apparatus according to claim 1,further comprising: a dividing unit configured to divide the pluralityof communication apparatuses into a plurality of groups, wherein aquantity of groups is configured to be represented by a number, whereinthe allocation unit allocates a communication slot during whichcommunication apparatus of a group transmits data to other communicationapparatus of another group, and wherein the allocation unit does notallocate a communication slot to the group positioned farthest from thecontrol apparatus when the number of groups is three or more.
 5. Thecontrol apparatus according to claim 1, wherein data includes data ofeach communication apparatus of the plurality of communicationapparatuses.
 6. The control apparatus according to claim 1, furthercomprising: a transmission unit configured to transmit data to theplurality of communication apparatuses at a predetermined communicationslot.
 7. The control apparatus according to claim 2, wherein thedetermination unit determines the relative position of eachcommunication apparatus of the plurality of communication apparatusesbased on a strength of a transmitted signal, on a transmission delay ofan acoustic signal or an ultrasonic signal from the communicationapparatus, or on an imaging result by an optical imaging unit.
 8. Acommunication apparatus, comprising: a receiving unit configured toreceive data in the course of a first communication slot, a secondcommunication slot, and a third communication slot, wherein, in thecourse of the first communication slot, the receiving unit receivesfirst data, which is directly transmitted from a first othercommunication apparatus to the communication apparatus, wherein, in thecourse of the second communication slot, the receiving unit receivessecond data, which is obtained by performing a relay transmission of thefirst data in a second other communication apparatus, and wherein, inthe course of the third communication slot, the receiving unit receivesthird data from a third other communication apparatus, the third databeing obtained by performing maximum likelihood processing based on thefirst data transmitted in the first communication slot and the seconddata transmitted in the second communication slot; and a first maximumlikelihood processing unit configured to perform maximum likelihoodprocessing based on the first data received in the course of the firstcommunication slot, the second data received in the course of the secondcommunication slot, and the third data received in the course of thethird communication slot.
 9. The communication apparatus according toclaim 8, wherein the receiving unit performs communication using TimeDivision Multiple Access, Code Division Multiple Access, FrequencyDivision Multiple Access, and/or Space Division Multiple Accesstechniques.
 10. The communication apparatus according to claim 8,further comprising: a control unit configured, in response to a requestfrom a control apparatus in a communication system to which thecommunication apparatus belongs, to generate information for estimatinga distance to another communication apparatus based on communicationwith that another communication apparatus and to control transmission ofthat information to the control apparatus.
 11. A communication system,comprising: a plurality of communication apparatuses including a firstcommunication apparatus, a second communication apparatus, and a thirdcommunication apparatus; a control apparatus including: an allocationunit configured to allocate: a first communication slot for the first,second, and third communication apparatuses to receive first datadirectly transmitted from a data source, a second communication slot forthe second and third communication apparatuses to receive second datatransmitted from the first communication apparatus, the second databeing obtained by performing a relay transmission of the first data inthe first communication apparatus, a third communication slot for thethird communication apparatus to receive third data transmitted from thesecond communication apparatus, the data being obtained by performingmaximum likelihood processing based on the first data transmitted fromthe data source in the first communication slot and the second datatransmitted from the first communication apparatus in the secondcommunication slot; and a notification unit configured to notify atleast the first, second, and third communication apparatuses of thecommunication slots allocated by the allocation unit, wherein each ofthe plurality of communication apparatuses includes: a receiving unitconfigured to receive a plurality of the data in the course of thefirst, second, and third communication slots, and a maximum likelihoodprocessing unit configured to perform maximum likelihood processingbased on the first data received in the course of the firstcommunication slot, the second data received in the course of the secondcommunication slot, and the third data received in the course of thethird communication slot.
 12. A control method for a control apparatusthat performs communication with a plurality of communicationapparatuses including a first communication apparatus, a secondcommunication apparatus, and a third communication apparatus, thecontrol method comprising: allocating: a first communication slot forthe first, second, and third communication apparatuses to receive firstdata directly transmitted from a data source, a second communicationslot for the second and third communication apparatuses to receivesecond data transmitted from the first communication apparatus, thesecond data being obtained by performing a relay transmission of thefirst data in the first communication apparatus, and a thirdcommunication slot for the third communication apparatus to receivethird data transmitted from the second communication apparatus, the databeing obtained by performing maximum likelihood processing based on thefirst data transmitted from the data source in the first communicationslot, the second data transmitted from the first communication apparatusin the second communication slot, and the third data transmitted fromthe second communication apparatus in the third communication slot; andnotifying at least the first, second, and third communicationapparatuses of the communication slots.
 13. A control method for acommunication apparatus, the control method comprising: receiving datain a course of a first communication slot, a second communication slot,and a third communication slot, wherein, in the course of the firstcommunication slot, first data is received, which is directlytransmitted from a first other communication apparatus to thecommunication apparatus, wherein, in the course of the secondcommunication slot, second data is received, which is obtained byperforming a relay transmission of the first data in a second othercommunication apparatus, and wherein, in the course of the thirdcommunication slot, third data is received, which is obtained byperforming a maximum likelihood processing based on the first datatransmitted in the first communication slot and the second datatransmitted in the second communication slot; and performing maximumlikelihood processing based on the first data received in the course ofthe first communication slot, the second data received in the course ofthe second communication slot, and the third data received in the courseof the third communication slot.
 14. A non-transitory computer readablestorage medium storing a program that, when executed by a computer,causes the computer to perform the control method according to claim 12.15. The control apparatus according to claim 6, wherein the transmissionunit transmits the data using Time Division Multiple Access, CodeDivision Multiple Access, Frequency Division Multiple Access, and/orSpace Division Multiple Access techniques.
 16. The control apparatusaccording to claim 6, wherein the notification unit uses a firstmodulation scheme and the transmission unit use a second modulationscheme that is different from the first modulation scheme.
 17. Thecommunication apparatus according to claim 8, further comprising: anacquisition unit configured to acquire a communication slot, which isallocated to that communication apparatus, and during which thatcommunication apparatus transmits the data; and a transmission unitconfigured to transmit the data, on which the maximum likelihoodprocessing has been performed by the maximum likelihood processing unit,to other communication apparatuses, during the communication slot thatis allocated to that communication apparatus.
 18. The communicationapparatus according to claim 17, wherein the acquisition unit furtheracquires a group to which that communication apparatus belongs.
 19. Thecontrol apparatus according to claim 1, wherein the data source is thecontrol apparatus.